1. Field of the Invention
The present invention relates to an optical disc apparatus for recording data into a plurality of optical discs, and particularly, to an optical disc apparatus including a cache HDD and an optical disc container cell, in addition to an optical disc drive.
2. Description of the Related Art
The amount of data which must normally be managed in an office has been increasing. To manage a great deal of data, many kinds of assembled optical disc apparatus have been proposed, which comprises a container cell for containing a plurality of portable optical discs each having a large capacity, a plurality of optical disc drives, and an accessor (or a so-called automatic changer) for moving the optical discs between the optical disc drives and the container cells.
When using the accessor, however, operations for moving and attaching an optical disc to an optical disc drive from an optical disc container cell and for detaching the disc from the cell require a relatively long time period in comparison with processing operations for reading and writing data. Therefore, "a control method for an assembled optical disc apparatus" was proposed in Jpn. Pat. Appln. KOKAI Publication No. 5-28615 and in this method, containing positions of optical discs are designed such that the distance through which discs are moved is as small as possible.
Further, since an optical disc drive requires a longer time to access a disc than a hard disc drive, an apparatus using a layered memory control method as described below has been practiced in order to achieve a high-speed access.
The apparatus using such a layered memory control method utilizes a characteristic that normally, several items of stored data are frequently accessed, while other items of stored data are not frequently accessed. For example, Nikkei Bite, issued in May, 1992, pages 211 to 213, describes a method in which data items which are frequently accessed are stored into a high-speed device, and data items which are not frequently accessed are stored into an optical disc. In this structure, it is possible to constitute an apparatus which requires lower costs than and apparatus comprised of only semiconductor memories and hard discs, and which achieves performance substantially equal to that of the latter apparatus.
In this kind of assembled optical disc apparatus, data can be stored in three different positions as follows, when access to data is carried out.
Position A: Upper layer memory portion accessed at a high speed, such as, a hard disc, a semiconductor memory, and the like.
Position B: Optical disc installed in an optical disc drive.
Position C: Optical disc in a container cell.
In the case of the position A, access can be achieved at the highest speed in the three positions. In general, an access operation of an optical disc drive is several times slower than that of a hard disc drive, so that access to data stored in the position B requires a time period several times longer to access data stored in position A.
In the case of the position C, when data is read or written, an optical disc previously installed in an optical disc drive must be detached therefrom, and then, an optical disc storing data to be accessed must be attached into the optical disc drive. Therefore, this operation takes a time period several hundred times longer than an operation for accessing data stored in position A. The main factors causing such a long operation are, for example, spin-down processing performed before detaching an optical disc from an optical disc drive (i.e., processing for stopping a motor which rotates an optical disc), and spin-up processing performed after attaching an optical disc to the optical disc drive (i.e., processing for increasing a rotation speed of a motor which rotates the optical disc, to a predetermined rotation speed.)
From the above, it is understood that a time period required for accessing data is extremely long when data to be accessed is stored in an optical disc contained in a container cell. Therefore, it is important to collect data items, which are frequently accessed, not only into the upper layer memory portion but also into an optical disc installed in the optical disc drive.
In a conventional assembled optical disc apparatus, data is stored without distinguishing positions A and B from each other. In other words, a conventional apparatus adopts a method in which data items which are frequently accessed are stored on a hard disc which serves as an upper layer memory portion, while the other data items are merely stored on optical discs. Therefore, whether or not a target disc to which a data item is to be accessed is installed in an optical disc drive is not determined. As a result, when a data item to be accessed is not stored in a hard disc, there is a relatively high possibility that optical discs are exchanged between the optical disc drive and a container cell, and thus, a conventional apparatus exhibits very low response performance.